1. Field of the Invention
The present invention relates to ignition timing control systems in spark ignition type internal combustion engines which have multiple cylinders, and particulrly to improvements in an ignition timing control system in a spark ignition type internal combustion engines, particularly suitable for use in a gasoline engine mounted on a motor car, wherein ignition pulses generated in accordance with the operating condition of the engine are delayed in response to knockings detected to control the ignition timings to the optimum advance conditions free from knockings.
2. Description of the Prior Art
In general, knockings in the internal combustion engines (hereinafter referred to as an "engine") are dangerous phenomena which may cause even a breakdown of the engine at the worst. Consequently, ignition timings of the engines have been controlled to the predetermined ignition timings in such a manner that the load and rotational number of the engine are measured and the values thus measured are utilized not to cause knockings to the engine. As such ignition timing control systems, heretofore, there have been used various types of systems including mechanical systems, electrical systems and the like. In any one of these systems the preset ignition timings have been set providing an allowance to a certain extent in ignition timing from the limits of knocking (the point where knocking takes place) because there have been dispersions in tolerances and adjustments of the system as a product. However, it is not desirable to provide an allowance in ignition timing from the limits of knocking from the viewpoint of economics of fuel consumption and possible loss in output power.
In recent years, in order to obviate the abovedescribed disadvantages, there has been developed an ignition timing control system in which knockings are detected by use of knocking sensors to detect the condition of the engine at the limits so that ignition timings can be feedback controlled to the optimum advance conditions free from knockings. The abovedescribed ignition timing control systems can eliminate the necessity of the provision of the allowance in the preset values of ignition timings which would otherwise have been necessary so that improvements in fuel combustion and the like can be expected therefrom. However, in the case of a multiple cylinder engine, there may be a wide dispersion in the limits of knocking because respective cylinders are different in quantity of intake air and air-fuel ratio of mixture from one another, in general. FIG. 1 shows the knocking occurring points differing from one cylinder to another in a six-cylinder engine, in which a solid line A shows the ignition timings where the knockings begin to occur. In this engine, there is a 10 degree difference in crank angle between the ignition timings at the maximum. If the abovedescribed knocking feedback control is effected in this condition, then, in order to detect occurrence of a knocking to control the ignition timings, an ignition timing for a cylinder following the cylinder of the knocking becomes an ignition timing for No. 1 cylinder having the latest ignition timing as indicated by a broken line B in FIG. 1, so that adverse effects may be caused to the fuel consumption and the like within the scope corresponding to a hatched region between the broken line B and the solid line A.